/usr/lib/x86_64-linux-gnu/pkgconfig/libstartup-notification-1.0.pc is in libstartup-notification0-dev 0.12-3ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir=${prefix}/include
Name: libstartup-notification
Description: Startup notification library
Version: 0.12
Libs: -L${libdir} -lstartup-notification-1
Cflags: -I${includedir}/startup-notification-1.0
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